TABLE 1.
Kinetic Analyses of O-glucuronidation of trans-4-OH-TAM or trans-Endoxifen by UGTsa
|
trans-4-OH-TAM |
trans-Endoxifen |
|||||
|---|---|---|---|---|---|---|
| UGT | Vmax (pmol min−1 μg−1)b | KM (μM) | Vmax/KM (μl min−1 μg−1)b | Vmax (pmol min−1 μg−1)b | KM (μM) | Vmax/KM (μl min−1 μg−1)b |
| 1A1 | 3.4 ± 0.2 | 124 ± 16 | 0.028 ± 0.004 | 2.3 ± 0.3 | 333 ± 60 | 0.007 ± 0.0005 |
| 1A3 | 1.9 ± 0.3 | 94 ± 17.8 | 0.02 ± 0.001 | 2.9 ± 0.4 | 158 ± 29 | 0.02 ± 0.001 |
| 1A7 | 1.2 ± 0.2 | 166 ± 27 | 0.0074 ± 0.0002 | low activityc | ||
| 1A8 | 3.2 ± 0.2 | 23 ± 2.4 | 0.14 ± 0.02 | 11.6 ± 1.4 | 101 ± 13 | 0.12 ± 0.01 |
| 1A9 | 3.0 ± 0.1 | 319 ± 38 | 0.009 ± 0.001 | low activityc | ||
| 1A10 | 4.7 ± 0.3 | 96 ± 8.0 | 0.049 ± 0.006 | 5.7 ± 0.7 | 40 ± 3.0 | 0.14 ± 0.005 |
| 2B7 | 0.55 ± 0.18 | 3.7 ± 0.6 | 0.15 ± 0.03 | 3.0 ± 0.4 | 101 ± 17 | 0.03 ± 0.004 |
| 2B17 | 0.02 ± 0.001 | 41 ± 6 | 0.001 ± 0.0001 | no detectable activityd | ||
a
All data are the mean ± SD based on three independent experiments.
b
Data are expressed per μg UGT protein as determined by Western blot analysis.
c
Low activity describes the fact that although some glucuronidation activity was observed for a UGT enzyme against a particular TAM metabolite, the level of detection was below sensitivity for kinetic studies.
d
In addition to no detectable glucuronidation activity observed for homogenates of UGT2B15-overexpressing cells observed against trans-endoxifen, homogenates from cells overexpressing UGTs 1A6, 2B4, 2B10, 2B11, or 2B15 exhibited no detectable glucuronidating activity against trans-4-OH-TAM or trans-endoxifen.